Thermoplastic mixture with high flexibility and high melting point

ABSTRACT

A thermoplastic mixture is described that includes at least one impact-resistant polypropylene copolymer and at least one ethylene-1-octene copolymer. The weight ratio of impact-resistant polypropylene copolymer to ethylene-1-octene copolymer can be in the range of 35:65 to 65:35. The thermoplastic mixture has a high melting point and excellent flexibility. The mixture is suitable in particular for roof membranes and waterproofing membranes.

TECHNICAL FIELD

The invention relates to a thermoplastic mixture and its use for roofingmembrane or waterproofing membrane.

PRIOR ART

The service temperatures of roof and motor vehicle applications such asroof or waterproofing membrane, for example, require materials with amelting point of at least 140° C. Polypropylene (PP) with a meltingpoint of approximately 160° C. is therefore a standard first-choiceplastic. Polyethylene (PE) with a melting point of at most 125° C. isnot suitable for this purpose. However, isotactic polypropylene (iPP) isa stiff polymer, and due to its relatively high glass transitiontemperature (Tg approximately 10° C.), it has a poor notch impactstrength, particularly at low temperatures. Therefore, iPP needs to bemade more flexible and tougher.

In order to make iPP tougher, a second domain, which may be organic orinorganic, can be incorporated in the polymer. The incorporation ofethylene monomers in the propylene base structure has been found to bethe most advantageous. Such polymers are well known commercial products,and they are referred to as statistical polypropylene copolymer orpolypropylene random copolymer (RACO; “random copolymer”) orimpact-resistant polypropylene copolymer (ICP; “impact copolymer”).However, these polypropylene copolymers still have a relatively highstiffness.

Also commercially available are complex impact strength-modifiedmixtures made of polypropylene, polyethylene and copolymers thereof,which are referred to as “reactor blends.” The polymers of thesemixtures are produced simultaneously in a multizone reactor. The polymermixtures obtained have a low modulus and thus a high flexibility and ahigher melting point, approximately 140° C., than PE. However, theirmelting point is thus approximately 20° C. lower than that of mixturesbased on iPP. Such polymer mixtures are commercially available under thename Hifax® from LyondellBasell.

PP homopolymers (iPP) and PP copolymers (RACO and ICP) have goodmiscibility with commercial ethylene-propylene copolymers such asVistamaxx® or Versify®, and they can be made flexible by the addition ofsuch ethylene-propylene copolymers. However, homopolymers or copolymersmade flexible in this manner are frequently brittle at low temperatures.

In order to make iPP, RACO and ICP flexible, the use ofethylene-alpha-olefin copolymers, also referred to as polyolefinelastomers (POE), has also been investigated. Nitta et al., Polymer, 39,53-58 (1998), investigated mixtures of iPP and ethylene-1-butenecopolymers. Yamagushi et al., J. Polym. Sci., 35, 953-961 (1997),produced mixtures of iPP and ethylene-1-hexene copolymers. In anotherstudy, Yamagushi et al., J. Appl. Polym. Sci., 62, 87-97 (1996),investigated the compatibility of mixtures of iPP and ethylene-propylenerubber.

U.S. Pat. No. 6,803,415 B1 describes mixtures of 10 to 90 wt % of arandom copolymer made of propylene and of a comonomer selected fromethylene and C₄-C₈ alpha-olefins with a melting point between 100° C.and 140° C., and 10 to 90 wt % of a random copolymer made of ethyleneand of a comonomer selected from C₃-C₁₀ alpha-olefins, which have acertain Mw/Mn ratio. Such mixtures are proposed for producing extrudedfilms and flexible cover films as well as for cables.

EP 0 605 180 A1 discloses polypropylene compositions made of 55 to 95parts by weight of polypropylene and 5 to 45 parts by weight of anethylene/1-butylene or ethylene/1-octene random copolymer. Thepolypropylene can be a random or block copolymer, wherein, however, theproportion of monomers other than propylene in the content should not bemore than 10 mol %. The mixtures are used in films, particularly in themotor vehicle field, where they can be used in the interior furnishingsor as decorative exterior elements.

Finally, US 2008/150261 describes partially crosslinked thermoplasticelastomer compositions which contain propylene/ethylene orpropylene/α-olefin copolymers having an impact strength of at least 30kJ/m², ethylene/α-olefin copolymers and thermoplastic elastomers as wellas additional crosslinking agents. Such compositions can be processed athigh production rates to form shaped parts, since the time required fromthe injection of the material to the sufficient hardening thereof isvery short.

DESCRIPTION OF THE INVENTION

The problem of the present invention consisted in providing a materialwith high service temperature or high melting point and highflexibility, which is suitable for roof or waterproofing membrane, forexample, for roof or motor vehicle applications. Surprisingly, athermoplastic mixture with high melting point and high flexibility isobtained, which, in addition, has excellent mechanical properties and avery advantageous glass transition temperature, if one mixes acommercial impact-resistant PP copolymer (ICP) with an ethylene-1-octenecopolymer in a certain ratio.

The invention therefore relates to a thermoplastic mixture whichcomprises at least one impact-resistant polypropylene copolymer and atleast one ethylene-1-octene copolymer, wherein the weight ratio ofimpact-resistant polypropylene copolymer to ethylene-1-octene copolymeris in the range from 35/65 to 65/35.

In addition to a relatively high melting point, the mixture according tothe invention has excellent properties with regard to thermal stability,flexibility and tensile strength, and it is therefore excellently suitedfor use in roofing membrane and waterproofing membrane.

The mixture according to the invention is a mixture of thermoplasticmaterials, in particular of the impact-resistant polypropylene copolymerand of the ethylene-1-octene copolymer. The mixture can contain one ormore types of impact-resistant polypropylene copolymers, wherein as arule only one type is used. The mixture can also contain one or moretypes of ethylene-1-octene copolymers, wherein as a rule only one typeis used. Thermoplastic mixtures are commonly also referred to asthermoplastic blends.

Impact-resistant polypropylene copolymer is a common commercial product.Polypropylene is offered commercially essentially in three productgroups, as PP homopolymer (hPP), as statistical polypropylene copolymer(RACO) and as impact-resistant polypropylene copolymer (ICP). Thecopolymers are copolymers of propylene with another olefin, as a ruleethylene. Impact-resistant polypropylene copolymer is based as a rule onisotactic polypropylene. Impact-resistant polypropylene copolymer isessentially a block copolymer of propylene and of an olefin such asethylene, butylene, hexene and/or octene, for example, preferablyethylene. Accordingly, random copolymers made of propylene and anadditional olefin should not be considered impact-resistantpolypropylene copolymers in the sense of this invention. Numerousvariants ranging from two-block to multi-block copolymers are known.Furthermore, variants with different numbers of blocks and/or differentmolecular weights are known. In addition to ICP, PP-B (polypropyleneblock copolymer) is also used as an abbreviated designation.

The incorporation of olefin monomers in a PP chain itself alreadyresults in an increase in the crystallization temperature. An additionalnucleation can be achieved, for example, by the addition of nucleatingagents. Impact-resistant polypropylene copolymer (ICP) is available asan impact-resistant polypropylene that is not additionally nucleated oras an impact-resistant polypropylene copolymer that is additionallynucleated (nICP). The use of nICP is preferable, since it has a lowermodulus. As a result, the mixing quality is improved, which also yieldsa further improved tensile strength. The modulus can also be customized,for example, by the use of mixtures made of ICP and nICP.

Ethylene-1-octene copolymer is also commercially available in differentvariants, for example, relating to the 1-octene content and themolecular weight. Such copolymers can be produced by metallocenecatalysis, for example. They are preferably copolymers with statisticaldistribution of the monomer units, which are also referred to as EOR(ethylene-1-octene random copolymer). The 1-octene content in theethylene-1-octene copolymer can vary in broad ranges, but it isappropriately in the range from 1 to 25 mol %, preferably 2 to 20 mol %,and particularly preferably 5 to 20 mol % or 7 to 18 mol %, wherein arange from 16 to 20 mol % is particularly suitable. The proportion of1-octene in the copolymer can be determined directly by ¹H-NMRspectroscopy. The person skilled in the art is familiar with thismethod. The content can also be determined by a density measurement.

As mentioned, the copolymers are commercially available, but they canalso be produced directly by the person skilled in the arthimself/herself. Commercial products for ICP and nICP are available fromExxonMobil, for example. Dow markets, for example, ethylene-1-octenecopolymers with different 1-octene contents as Engage®8450, Engage®8200and Engage®8842. ExxonMobil markets ethylene-1-octene copolymers underthe name “Exact Plastomers” Information on the production and on theproperties of impact-resistant polypropylene copolymers can be obtainedfrom US 2002086947 A1, for example, and of ethylene-1-octene copolymersfrom Weaver, L B. et al., “A New Class of Higher Melting PolyolefinElastomers for Automotive Applications,” Proceedings of the SPEAutomotive TPO Global Conference, 2006, for example.

The weight ratio of impact-resistant polypropylene copolymer toethylene-1-octene copolymer is in the range from 35/65 to 65/35,preferably in the range from 40/60 to 60/40. The best properties areachieved with a weight ratio of impact-resistant polypropylene copolymerto ethylene-1-octene copolymer of approximately 50/50, that is, forexample, in the range from 45/55 to 55/45.

In a particularly preferable embodiment, the weight ratio ofimpact-resistant polypropylene copolymer to ethylene-1-octene copolymeris in the range from 45/55 to 55/45, wherein the ethylene-1-octenecopolymer has a 1-octene content of 16 to 20 mol %.

Using the mixing ratio adjusted according to the invention, a truemixture, i.e., a single phase, with a peak glass transition temperature(Tg) of approximately −25° C. can be achieved, which is unique for thiscomposition. A corresponding mixed phase can also be found in “reactorblends,” but to date not in polymer blends produced in the melt. Acommon phase is not obtained in the case of mixtures having the weightratio of 70/30 or 30/70 of impact-resistant polypropylene copolymer toethylene-1-octene copolymer. A single phase is also not obtained if hPPis used instead of ICP or nICP.

The melt flow index (MFI) of the ethylene-1-octene copolymer can vary inbroad ranges. A suitable range for the MFI of the ethylene-1-octenecopolymer used is, for example, 0.2 to 30 g/10 min, preferably 0.5 to 15g/10 min. The MFI can be determined at 190° C., 2.16 kg in accordancewith the standard ASTM D1238. The MFI of the impact-resistant PPcopolymer can also vary within broad ranges. A suitable range for theMFI of the impact-resistant PP copolymer used is 1 to 16 g/10 min, forexample. The MFI can be determined at 230° C., 2.16 kg according to thestandard ISO 1133.

The thermoplastic mixture can consist of only impact-resistantpolypropylene copolymer and ethylene-1-octene copolymer. However, one ormore additives can also be added to the thermoplastic mixture, whereinthe quantity thereof can be within the usual range. The proportion ofimpact-resistant polypropylene copolymer and ethylene-1-octene copolymertogether in the thermoplastic mixture can vary, but in general it is atleast 40 wt %, preferably at least 50 wt %, and particularly preferablyat least 60 wt % of the thermoplastic mixture.

All the additives or admixtures that are suitable for the thermoplasticmixture and commonly used in PP homopolymers and PP copolymers, inparticular for ICP, can be used. The selection of the optionally usedadditives depends on the intended purpose of use. Examples of additivesare stabilizers such as antioxidants, for example, sterically hinderedphenols, hydrazones or bishydrazones, UV stabilizers, for example,alkoxyhydroxybenzophenones and HALS stabilizers, heat stabilizers, lightstabilizers, color acceptors such as pigments or dyes, crystalnucleating agents such as mono-, di- or polycarboxylic acids and theirsalts, antistatic agents such as compounds with hydroxyl, amino or amidegroups, plasticizers, lubricants such as fatty acid salts, fatty acidesters or fatty acid amides, hydrophobizing agents, compatibilizers,biocides and flame retardants.

As additional additives, fillers and other polymers can be considered.Commonly used fillers are, for example, chalk, fly ash, wood meal, glassfibers, glass beads and talc. Other polymers can be used, for example,as compatibilizers. Examples of compatibilizers are ethylene-propylenerubbers (EPR) or ethylene-propylene-diene rubbers (EPDM), which caninfluence the mechanical properties such as the impact resistance.

In individual cases, the thermoplastic mixture can also containcrosslinked thermoplastic elastomers, for example, in the form of SBS(styrene-butadiene-styrene), SEBS (styrene-ethylene/butadiene-styrene),SEPS (styrene-ethylene/propylene-styrene) or SEP(styrene-ethylene/propylene). However, it is preferable for the amountof such thermoplastic elastomers to be, to the extent possible, not morethan 5 wt % relative to the total weight of the thermoplastic mixture,since, as a result of an excessively high proportion of such polymers,the welding of, for example, roofing membrane produced from the mixturecan no longer be guaranteed. Therefore, it is preferable for thethermoplastic mixture to contain less than 1 wt % of crosslinkedthermoplastic elastomers, and particularly preferably to be free ofcrosslinked thermoplastic elastomers.

Using crosslinking agents, it is also possible to crosslink thethermoplastic mixture, which would affect the weldability of productsprepared from the mixture. Accordingly, the thermoplastic mixtures canindeed in principle also contain crosslinking agents, in particular freeradical formers such as peroxides or photoinitiators, as additives;however, it is preferable for the proportion of such crosslinking agentsto be as small as possible, i.e., less than 1 wt % relative to the totalweight of the thermoplastic mixture. It is particularly preferable forthe thermoplastic mixture to be free of crosslinking agents or for thethermoplastic mixture to be a crosslinking agent-free thermoplasticmixture.

All or some of the additives can naturally already be contained in thestarting materials used, for example, in the ethylene-1-octene copolymeror preferably in the impact-resistant PP copolymer. Furthermore, theadditives can also be added in the process of mixing the copolymerstarting materials. They can also be added in a subsequent compoundingstep, for example, in a second extruder or simply by mixing into thepowder of the thermoplastic mixture obtained. The preparation of thethermoplastic mixture occurs by conventional methods known to the personskilled in the art. The starting materials can be introduced, forexample, in the form of powder, granulate or pellets into a mixingdevice and mixed at elevated temperature, for example, in the range from180 to 300° C. As mixing device, it is appropriate to use an extruder,for example, such as a single-screw or preferably a twin-screw extruderin which the starting materials are plasticized and mixed at elevatedtemperature. The mixture can then be extruded through a nozzle andgranulated with a cutting device. The mixture can thus be obtained asgranulated product, for example, as granulate or powder or pellets.

The thermoplastic mixture according to the invention is particularlysuitable for roof or motor vehicle applications, wherein roofapplications are preferable. The thermoplastic mixture is preferablyused for roofing membrane or waterproofing membrane or sealingmembranes.

Roofing membrane and waterproofing membrane comprise or consist ofplastic sheeting for the manufacture of which the thermoplastic mixtureof the present invention is suitable.

The terms roofing membrane and waterproofing membrane in this documentrefer particularly to flexible flat plastics with a thickness from 0.1to 5 mm, in particular 0.5 to 4 mm, which can be rolled up. Thus, inaddition to films in the strict sense, which have thicknesses of lessthan 1 mm, it is possible also, and in particular preferable, to usewaterproofing membrane as used typically for the sealing of roofs orterraces, which has a thickness of typically 1 to 3 mm, in special caseseven a thickness of at most 5 mm. Such membranes are usually produced byspreading, casting, calandering or extrusion, and they are typicallycommercially available in rolls or produced on site. They can have asingle layer or a multiple layer structure. It is clear to the personskilled in the art that such membranes in addition can contain otheradditives and processing agents such as fillers, UV and heatstabilizers, plasticizers, lubricants, biocides, flame retardants andantioxidants. Pertinent examples have been mentioned above. Additionaladditives, as described above for example, can also be part of thecontent.

EXAMPLES

Below some examples are indicated, which further illustrate theinvention but are not intended to limit the scope of the invention inany way. Unless otherwise indicated, the proportions and percentagesrefer to the weight.

For the determination of the 1-octene content in the ethylene-1-octenecopolymer, ¹H-NMR spectroscopy was carried out with a Bruker Ultrashield300 MHz. 30-35 mg of a sample of the copolymer were dissolved in 0.7 mLof 1,2-dichlorobenzene-d4 for 2 hours at 150° C. in the microwave ovenand 256 scans were accumulated at 130° C. For the calculation of the1-octene content, the following formula was used:

$\frac{\frac{I\text{?}}{3}}{{\frac{I\text{?}}{2} \cdot \left( {1 - {\frac{1}{3}x}} \right)} + \frac{I\text{?}}{3}} = {\frac{1}{3}x}$?indicates text missing or illegible when filed                    

where I_(CH3) corresponds to the integral of the peak at 0.9 ppmassigned to the methyl terminal group, and I_(CH2) corresponds to theintegral of the peak at 1.3 ppm which is assigned to the H atoms of theCH2 groups of the base structure and of the 1-octene side chains, and xcorresponds to the content of 1-octene in mol %. The measured peakpositions correspond to the data in the literature.

The following compounds were used as starting materials. The MFI of thepolypropylene-containing homopolymers and copolymers was measured at230° C./2.16 kg. The MFI of the ethylene-1-octene copolymer wasdetermined at 190° C./2.16 kg.

-   PP7043L1 IPC (impact-resistant PP copolymer) from ExxonMobil, MFI=8    g/10 min, Mw≈398,000 g/mol-   PP8013L1 nIPC (nucleated impact-resistant PP copolymer) from    ExxonMobil, MFI=8 g/10 min, Mw≈344,000 g/mol-   PP1063L1 hPP from ExxonMobil, MFI=8 g/10 min, Mw≈477,000 g/mol-   Engage®8842 EOR18, ethylene-1-octene copolymer from DOW, MFI=2 g/10    min, Mw≈176,000 g/mol, 1-octene content=17.9 mol %-   Hifax® CA212 thermoplastic polyolefin (reactor blend of polyethylene    and polypropylene), MFI=8 g/10 min

The starting polymers were mixed in the mixing ratios indicated in thetable below. For this purpose, the polymers were compounded in aco-rotating twin-screw extruder having a cavity volume of approximately5 cm³. The mixing was carried out at a shear rate of 100 rpm at 200° C.for 20 min. Subsequently, the polymer melt was released from theextruder and cooled in air. All the tests were carried out in a nitrogenatmosphere. The samples obtained were investigated with the followingmethods.

Thermal Analysis

The melting points and crystallization temperatures were determinedusing a differential scanning calorimeter (DSC) from Mettler Toledo, DSC882^(e). The melting points were determined from the first heating passfrom −30° C. to 200° C. at a heating rate of 10° C. min⁻¹ (sample weightapproximately 10 mg). The crystallization temperatures were determinedfrom the first cooling pass from 200° C. to −30° C. at a cooling rate of10° C. min⁻¹.

Dynamic Mechanical Analysis

DMA measurements were conducted with a Mettler Toledo DMA/SDTA 861^(e).The glass transition temperatures were determined from the phase angletan δ which corresponds to the ratio of the loss modulus to the storagemodulus. The samples were heated from −90° C. to 200° C. at a heatingrate of 5° C. min⁻¹. The frequency was kept constant at 1 Hz, while themaximum force amplitude and the maximum displacement were limited to 10N and 5 μm, respectively. The shear deformation was between 0.25 and0.5%.

TABLE Example 3* 4 5* 6 7* 8* 1* 2* ICP/ ICP/ ICP/ nICP/ hPP/ Hifax ICPEOR18 EOR18 EOR18 EOR18 EOR18 EOR18 CA212 Weight ratio 70/30 50/50 30/70 50/50  50/50 DMA Peak glass transition temperature [° C.] (−50/10) −45−50 −25 −45 −27 −50 −22 DSC Peak melting point [° C.] 166 38 166/40  166165/39  165/44 165/35 145/40 Peak crystallization temperature [° C.]115/94 22 120/75/20 120/75  120/75/20 124/76 124/21 100/75 *notaccording to the invention

FIG. 1 shows the mechanical loss factor as a function of the temperaturefor different mixing ratios of ICP and EOR18. FIG. 2 shows themechanical loss factor as a function of the temperature for hPP,Hifax®CA212, and a 50/50 mixture of nICP and EOR18. In FIG. 3, thetensile strength is shown as a function of the content of EOR18 innICP/EOR18 mixtures.

The impact-resistant PP copolymer shows improved compatibility withEOR18 compared with hPP. Mixtures of ICP with EOR18 in the ratio 50/50show no crystallization at approximately 20° C. (DSC) and a singlerelaxation peak at −25° C., which indicates miscibility of the twocopolymers in one phase.

1.-9. (canceled)
 10. A thermoplastic mixture obtained by mixing at leastone impact resistant polypropylene copolymer (ICP) and at least oneethylene-1-octene copolymer; wherein the mixture has a weight ratio ofimpact-resistant polypropylene copolymer to ethylene-1-octene copolymerin a range of from 35/65 to 65/35; and wherein the impact-resistantpolypropylene copolymer is based on an isotactic polypropylene.
 11. Thethermoplastic mixture according to claim 10, wherein the isotacticpolypropylene has a melt flow index (MFI) of 8 g/10 min to 16 g/10 mindetermined at 190° C., 2.16 kg with a standard ASTM D1238.
 12. Thethermoplastic mixture according to claim 10, wherein the ICP is an ICPthat is not additionally nucleated, an ICP that is additionallynucleated (nICP), or a mixture thereof.
 13. The thermoplastic mixtureaccording to claim 10, wherein the weight ratio of impact-resistantpolypropylene copolymer to ethylene-1-octene copolymer is in the rangeof from 45/55 to 55/45.
 14. The thermoplastic mixture according to claim10, wherein the ethylene-1-octene copolymer comprises from 16 mol % to20 mol % of 1-octene.
 15. The thermoplastic mixture according to claim10, wherein the mixture has a glass transition temperature (Tg) of about−25° C.
 16. The thermoplastic mixture according to claim 10, wherein themixture is obtained by additionally mixing at least one additiveselected from the group consisting of an antioxidant, a UV stabilizer, aheat stabilizer, a light stabilizer, a color acceptor, a crystalnucleating agent, an antistatic agent, a plasticizer, a lubricant, ahydrophobizing agent, a compatibilizer, a biocide, and a flameretardant.
 17. The thermoplastic mixture according to claim 10, whereinthe mixture is obtained by additionally mixing at least one fillerselected from the group consisting of a chalk, a fly ash, a wood metal,a glass fiber, a glass bead, and talc.
 18. The thermoplastic mixtureaccording to claim 10, wherein the mixture is obtained by additionallymixing at least one crosslinked thermoplastic elastomer.
 19. Thethermoplastic mixture according to claim 18, wherein the crosslinkedthermoplastic elastomer is styrene-butadiene-styrene (SBS),styrene-ethylene/butadiene-styrene (SEBS),styrene-ethylene/propylene-styrene (SEPS), or styrene-ethylene/propylene(SEP).
 20. The thermoplastic mixture according to claim 18, wherein thethermoplastic mixture comprises less than 1 wt %, relative to the totalweight of the thermoplastic mixture, of the crosslinked thermoplasticelastomer.
 21. The thermoplastic mixture according to claim 18, whereinthe mixture further comprises at least one crosslinking agent.
 22. Thethermoplastic mixture according to claim 21, wherein the crosslinkingagent is a peroxide or a photoinitiator.
 23. The thermoplastic mixtureaccording to claim 21, wherein the thermoplastic mixture comprises lessthan 1 wt % relative to the total weight of the thermoplastic mixture ofthe crosslinking agent.
 24. The thermoplastic mixture according to claim10, wherein the thermoplastic mixture that is obtained is a granulatedproduct.
 25. A method of producing a thermoplastic mixture, the methodcomprising mixing at least one impact-resistant polypropylene copolymer(ICP) and at least one ethylene-1-octene copolymer.
 26. The methodaccording to claim 25, wherein the ICP and the ethylene-1-octenecopolymer are in the form of a powder, a granulate, a pellet, ormixtures thereof.
 27. The method according to claim 25, wherein themixture is obtained by mixing the ICP and the ethylene-1-octene with anextruder device.
 28. The method according to claim 25, wherein themixture is obtained by mixing at a temperature in the range of from 180°C. to 300° C.
 29. The method according to claim 25, wherein the ICP isan ICP that is not additionally nucleated, an ICP that is additionallynucleated (nICP), or a mixture thereof.